import Mathlib.Tactic
/-!
# USA Mathematical Olympiad 2015, Problem 1
Solve in integers the equation x² + xy + y² = ((x + y) / 3 + 1)³.
-/
namespace Usa2015P1
/- determine -/ abbrev SolutionSet : Set (ℤ × ℤ) := sorry
theorem usa2015_p1 (x y : ℤ) :
⟨x, y⟩ ∈ SolutionSet ↔
x^2 + x * y + y^2 = ((x + y) / (3 : ℚ) + 1)^3 := sorry
end Usa2015P1
This problem has a complete formalized solution.